If x varies directly with y and y is 10 when x is 8, what is x when y is 18?

Knowing that x varies directly with y, we know the basic skeleton of the equation is y = mx. 

To find m, plug in the known coordinate (8,10), where the x-coordinate is 8 and the y-coordinate is 10.


Then, plug in m to the equation to get y = (5/4)x.

Finally, plug in the y-coordinate 18 to the equation and solve for x!


Your exact answer is x = 72/5. However, if your teacher prefers decimals, then x = 14.4

Hope this helps!